Bridging the Legacy Divide in AP Automation

Finance leaders are under increasing pressure to automate. Faster close cycles, tighter compliance requirements, and the push for “touchless” AP are driving automation from a “nice-to-have” into a necessity.

But there’s a problem: not every business runs on a modern ERP. In fact, many mid-sized and enterprise organisations still rely on finance systems that were implemented 10, 15, or even 20 years ago.

These legacy systems weren’t built with automation in mind. They were designed for stability, not flexibility. They don’t always speak the language of APIs. Their data structures are rigid. And yet, they are too entrenched and too costly to replace overnight.

This is the legacy divide: finance leaders want modern AP automation, but their core systems are firmly rooted in the past. The good news? Bridging this divide is possible. With the right approaches, businesses can unlock automation value today, while extending the life of their existing systems.

Why Legacy Systems Still Dominate

If legacy ERPs are holding businesses back, why haven’t more companies replaced them? The reality is more complex.

1. ERP replacement cycles are long and costly. For many, a full system replacement runs into millions of dollars and years of disruption.

2. Heavy customisation makes systems sticky. Over time, businesses have tailored their ERPs to fit unique processes. Those customisations are hard to walk away from.

3. Finance leaders prefer incremental improvements. Risk appetite is low; it feels safer to add bolt-ons than to overhaul the system.

4. “If it isn’t broken…” thinking. Legacy systems may lack modern features, but they remain stable, familiar, and reliable.

In short, replacing the ERP isn’t always realistic. But standing still isn’t an option either. Continuing with manual AP processes only carries inefficiency forward year after year.

The Real Integration Challenge

Legacy ERPs create several specific hurdles for AP automation:

• Rigid data structures: Older systems often have closed schemas that don’t align with modern AP outputs, making mappings complex.

• Limited connectivity: Many lack APIs altogether, relying instead on flat file imports or nightly batch jobs.

• High IT dependency: Any integration typically requires custom development from internal IT or external consultants.

• Workarounds and shadow systems: Without proper integration, finance teams resort to spreadsheets, duplicate data entry, or bolt-on tools that undermine data integrity.

The result is a patchwork environment where automation either stalls or creates as many headaches as it solves.

Modern Integration Approaches

Thankfully, technology has evolved. A range of approaches can now bridge the gap between modern AP automation platforms and older finance systems.

1. APIs Where Possible

Even some legacy ERPs have been retrofitted with partial API capabilities. When available, APIs are the preferred route, enabling near real-time data exchange and reducing reliance on flat files.

For AP teams, this means invoices are routed directly into the ERP as soon as they’re approved, with status updates syncing back automatically.

2. Middleware & Integration Layers

When APIs aren’t available, middleware can serve as the translator. Integration platforms (iPaaS solutions) or pre-built ERP connectors map AP outputs into the formats legacy systems expect.

This reduces the need for custom development, standardises data flows, and scales across multiple systems, a critical factor for businesses running more than one ERP.

3. Data Normalisation

Legacy systems often treat suppliers, GL codes, and currencies in inconsistent ways. Without normalisation, errors multiply as data flows in from AP.

A data normalisation layer ensures that supplier IDs, tax codes, and accounting structures align before transactions reach the ERP. This prevents reconciliation headaches later and provides accurate reporting.

4. Hybrid Batch + Real-Time Models

Some legacy systems simply can’t handle real-time posting. In these cases, hybrid models can be effective, offering real-time integration for critical workflows alongside nightly batch uploads for bulk data.

This balance allows finance leaders to reap the benefits of faster processing without overwhelming older systems.

Best Practices for Change Management

Technology alone won’t solve the legacy divide. Integration projects succeed when they’re supported by thoughtful change management.

• Engage IT and Finance together: Integration isn’t just a technical task; it changes workflows and responsibilities. Both teams must collaborate from day one.

• Map current processes first: Automating a broken or inefficient process only embeds the problem. Identify bottlenecks before building integrations.

• Pilot with a controlled scope: Start small. Select one supplier group, entity, or process to test before rolling it out more widely.

• Prioritise auditability: Integrations should enhance compliance, not bypass it. Ensure every automated posting leaves a clear audit trail.

• Plan for long-term support: Legacy ERPs won’t disappear overnight. Build integrations that are maintainable, with clear ownership for ongoing support.

The Strategic Payoff

Bridging the legacy divide isn’t just about saving time. Done right, it delivers significant business benefits:

• Faster invoice cycles, approvals, and postings happen without waiting for manual entry.

• Reduced errors, data flows directly, eliminating rekeying mistakes.

• Improved reporting, with normalised data, finance leaders gain a clearer view of spend.

• Deferred ERP replacement and automation extend the life and value of existing systems.

• Stronger supplier confidence, more consistent, accurate payments build better relationships.

This is the key: integration doesn’t just enable automation. It transforms how finance interacts with its suppliers, auditors, and executives.

Where Acume’s Perspective Fits

At Acume, we see legacy integration as the real frontier of AP automation. AI and next-generation analytics may grab headlines, but the day-to-day barrier for many businesses is far more practical: how to make modern automation work with the systems they already have.

That’s why we’ve built experience across dozens of ERP and finance system integrations, many of them with limited or no API support.

Our approach centres on:

• Structured business rules to govern every transaction.

• Data mapping and normalisation to ensure accuracy.

• Compliance-first workflows that leave a clear audit trail.

The result? Customers can unlock automation benefits now, without waiting for a costly ERP replacement project.

Conclusion: Don’t Let Legacy Mean Lagging

Legacy systems aren’t going away anytime soon. But that doesn’t mean finance leaders are stuck with manual, inefficient AP.

By leveraging APIs where they exist, using middleware when they don’t, and normalising data at every step, businesses can bring automation into even the most rigid ERP environments. Add in smart change management and a compliance-first mindset, and the payoff is faster cycles, fewer errors, and stronger supplier relationships.

Legacy shouldn’t mean lagging. The technology exists to bridge the divide – it’s time to use it.